This invention relates to an autotensioner for adjusting the tension in a timing belt or chain used with an automotive engine, or belts for driving engine auxiliaries.
FIGS. 13 and 14 show one of such conventional autotensioners.
This autotensioner has a pulley 52, a rolling contact bearing 53 rotatably supporting the pulley 52, and a pivot shaft 55 fixed to the inner ring of the rolling bearing 53. The pivot shaft 55 has a hole 54 having its axis offset from the axis of the bearing 53. The rolling bearing 53, the pivot shaft 55 and a cylinder 57 with a built-in hydraulic damper mechanism are fixed to the fixed member 51 such as an engine block. It has a rod 56 movable into and out of the cylinder and pressed against a stopper 58 protruding from an end of the pivot shaft 55.
When the pulley 52 pivots following the slackening of the belt, the rod 56 protrudes quickly, eliminating any gap between the rod and the stopper 58. When the tension in the belt increases, the rod 56 is pushed by the stopper 58 of the pivot shaft 55 and retracts slowly into the cylinder 57 due to the damping action of the hydraulic damper. The autotensioner is thus capable of keeping the tension in the belt constant.
With this type of conventional autotensioner, it is necessary to provide a gap G between the pulley 52 and the fixed member 51 in order to accommodate the cylinder 57 with the built-in hydraulic damper and the stopper 58 provided on the end of the pivot shaft 55 and adapted to be brought into contact with the rod 56 of the cylinder 57. The gap G adds to the height of the entire autotensioner.
Such a tall autotensioner cannot be mounted on an engine having only a limited space between the belt and the engine block.
An object of this invention is to provide an autotensioner which is low in height and which has a damper and a pulley support portion in a compact structure.